The verse that we studied previously is from Psalms 48. We read this Psalms chapter every Monday at the end part of the morning prayer, drawing the Light from world of Beriah (Creation) to the world of Yetzirah (Formation), connecting to Malchut, the world of Asiah (Action).
Monday represents the Left column, Gevurah and when God created this day, he didn’t say “it was Good” as in the other days.

Song of Songs 2:6
“שְׂמֹאלוֹ תַּחַת לְרֹאשִׁי, וִימִינוֹ תְּחַבְּקֵנִי”
“His left hand is under my head, and his right hand embraces me!”
Rabbi Ashlag explains that on the Left column Chokmah is going down to Malchut. He explains that even though the second day is very important, it doesn’t say “Good” because Chokmah and Malchut expected to separate from each other.

In the process of creation the light from the Endless went down into the empty space created as preparation for the creation of the 4 worlds. In an evolving process the different vessels of light/Sefirot were created by pushing and returning light. Malchu experienced all the Lights from above it and on the second day Chokmah was in Malchut while connected to Zeir Anpin. They were as one unit (Partzuf) and that wasn’t good because the plan of creation was to separate the ‘head’ (Keter, Chokmah and Binah) from the ‘end’ (Malchut) . For that reason, the second day wasn’t described as “Good”.

After Chokmah left the vessel of Malchut, it also disconnected it from Zeir Anpin. Now the process of work began to appear in the world.

The third day brought the balance between the Right and the left allowing them to connect together and bridge the upper level for “Greatness”. On this day God said twice ‘good’.

I guess that for some of the readers, this explanation would be hard to comprehend. I will try making a video to explain the process of creating the vessels and the Sefirot in the near future.
Please submit questions in the comments section below.